EP0248306A2 - Method and apparatus for blow-moulding curved plastics articles - Google Patents

Abstract

During blow molding of curved plastic hollow bodies, the parison is first extruded as a whole in a substantially straight line and vertically from top to bottom. The parison is then severed from the extrusion die and the severed parison precurved. Finally, the precurved parison is inserted as a whole into the blow mold and blown. An apparatus for carrying out this method comprises releasable support means for accommodating and holding the parison, curving means for preliminary curving of the parison, tilting means for tilting the support means into the horizontal position and a blow mold, the precurved parison being placed as a whole in one mold half of this blow mold.

Description

The invention relates to a method according to the preamble of patent claim 1. Furthermore, the invention relates to a device according to the preamble of patent claim 2.

In a known method and a known device of this type (JP-PA 53-121062), the extruded preform still connected to the extruder nozzle is gripped at its lower, free end by a retaining bolt, is bent into a U-shape by moving the bolt and is bent on the Fixed inner surface of one mold half. In this way, however, only curvatures of the preform can be achieved in one plane, but not in three-dimensional space.

In a further known method for blow molding curved hollow bodies made of plastic (DE-PS 29 27 098), the preform is immediately inserted into a two- or three-dimensionally curved mold cavity of a lower mold half during its extrusion, for which purpose either the mold halves or the nozzle must be moved accordingly. The disadvantage here is that large masses have to be moved, namely in one The lower half of the mold and in the other case the entire extruder carrying the nozzle. In addition, the lower part of the preform, which is inserted into the lower mold half, cools down more than the still exposed upper section, so that after the upper mold half has been applied, an irregularly heated molded part must be inflated, which can lead to imperfectly blown hollow bodies with different wall thicknesses .

It is an object of the invention to remedy these shortcomings and to propose a generic method in which the preform can be curved three-dimensionally, no large masses have to be moved and the preform does not experience essentially any different cooling during the bending process.

The object is achieved by the characterizing features of claim 1.

A device for carrying out the method according to the invention is the subject of claim 2. Features of preferred embodiments of this device are set out in subclaims 3 to 6.

• Fig. 1 eine schematische Seitenansicht einer Vorrichtung zum Blasformen von gekrümmten Kunststoff-Hohlkörpern;
• Fig. 2 und 3 schematisch verschiedene Seitenansichten einer Aufnahmeeinrichtung zum Aufnehmen und Festhalten eines schlauchförmig extrudierten Vorformlings;
• Fig. 4 eine Schnittansicht entlang der Linie 4-4 in Fig. 3;
• Fig. 5 eine Ansicht ähnlich Fig. 3 mit gekrümmter Aufnahmeeinrichtung;
• Fig. 6 die Aufnahmeeinrichtung nach ihrer Verschwenkung in die Horizontale;
• Fig. 7 eine Ansicht ähnlich Fig. 6 nach Überführung des Vorformlings von der Aufnahmeeinrichtung in die untere Formhälfte einer Blasform;
• Fig. 8 eine Ansicht ähnlich Fig. 7 mit einer oberen Formhälfte der Blasform;
• Fig. 9 eine andere Ausführungsform einer Aufnahmeeinrichtung für den Rohling mit Mitteln zum Vorkrümmen des Rohlings;
• Fig. 10 die Einrichtung aus Fig. 9 in einer anderen Arbeitsstellung; und
• Fig. 11 eine Schnittansicht entlang der Linie 11-11 in Fig. 10.

The following description of preferred embodiment Forms of the invention serves in connection with the accompanying drawing for further explanation. Show it:

• Figure 1 is a schematic side view of a device for blow molding of curved plastic hollow bodies.
• Figures 2 and 3 schematically different side views of a receiving device for receiving and holding a tubular extruded preform.
• Fig. 4 is a sectional view taken along line 4-4 in Fig. 3;
• 5 shows a view similar to FIG. 3 with a curved receiving device;
• 6 shows the receiving device after it has been pivoted into the horizontal;
• FIG. 7 is a view similar to FIG. 6 after the preform has been transferred from the receiving device into the lower mold half of a blow mold;
• 8 is a view similar to FIG. 7 with an upper mold half of the blow mold;
• Fig. 9 shows another embodiment of a receiving device for the blank with means for pre-bending the blank;
• 10 shows the device from FIG. 9 in a different working position; and
• 11 is a sectional view taken along the line 11-11 in Fig. 10th

1 schematically shows an extruder 1, which is arranged together with a blow mold 2 on a common machine frame 3. Plastic material entered into a hopper 4, for example polyethylene or polypropylene, is melted in a known manner in the extruder and fed via a screw conveyor (not shown) to a nozzle 5 with an internal mandrel, from which the plastic emerges vertically from top to bottom in the form of a tubular preform 6 of a certain length . After the desired extrusion length of the preform 6 has been reached, it is cut off at its upper end by the nozzle 5. This state is shown in Fig. 1.

The tubular preform is extruded from the nozzle 5 along a receiving device 7, which is shown in a front view as viewed along the arrows 2 in FIG. 1 in FIG. 2. In the embodiment shown, the receiving device 7 comprises a strip consisting of two essentially straight parts 8, 9, which are connected to one another in an articulated manner and whose cross-sectional shape can be seen in FIG. 4. Both Strip parts 8, 9 have a longitudinally extending cavity 11, which is closed at the upper and lower ends and which can be connected via nipples 12, 13 to a vacuum source (not shown). Bores 14 lead from the cavity 11 to the front of the strip parts 8, 9.

The articulation of the two parts 8, 9 is such that a relative pivoting in the plane of the drawing in FIG. 2 is possible, as indicated by dash-dotted lines.

One strip part 8 is connected to the shaft 15 of an electric motor 16, which in turn is supported on a bracket 17 of the machine frame 3. With the aid of the motor 16, the strip-shaped receiving device 7 can be pivoted from the illustrated vertical position into a horizontal position indicated by dash-dotted lines in FIG. 1 and back again, the pivoting taking place in the direction of the double arrow A in FIG. 1.

The relative pivoting of the two strip parts 8, 9 takes place by means known per se, not shown, for example pneumatically.

As shown, the preform 6 is extruded from the nozzle 5 along the receptacle 7 in the immediate vicinity of the outer openings of the bores 14 which can be displaced under vacuum. When the preform 6 is extruded to the desired length along the receptacle 7, the cavity 11 in the welt parts 8.9 are under vacuum, so that the tubular preform 6 is sucked in and held on the receiving device 7.

The cutting means 18, known per se and indicated in FIGS. 3 and 5, is then used to separate the upper end of the preform 6 from the nozzle 5.

The preform 6 is then pre-curved by pivoting the lower strip part 9 in the manner shown in FIG. 5.

Then, by actuating the motor 16, the receiving device 7 together with the preform 6 held thereon is pivoted through 90 ° along the arrow B into the horizontal (FIG. 6).

As can be seen from FIGS. 1 and 6, the lower mold half 21 of a blow mold with a mold recess 20 is arranged below the nozzle 5 and the receiving device. The spatial course of the mold recess 20 corresponds to the shape of the pre-curved preform 6 (FIG. 5).

By switching off the negative pressure in the receiving device 7, the pre-curved preform 6 is now allowed to fall into the lower mold half 21. Then - cf. Fig. 8 - the lower mold half 21 with an upper mold half 22, which has a corresponding recess 20, brought together. After the upper mold half 22 has been placed on the lower mold half 21, the preform 6 is inflated to the desired hollow body shape in a manner known per se.

As shown in FIG. 1, the upper mold half 22 can be moved up and down by means of a piston-cylinder unit 23 attached to the machine frame 3. The lower mold half 21, which is initially located below the receiving device 7 (shown in broken lines in FIG. 1), is brought under the upper mold half 22 with the preform 6 that has been introduced. The upper mold half 22 is then lowered onto the lower mold half and the preform 6 is inflated.

As shown and described, only the lower strip part 9 of the receiving device 7 has to be pivoted when the preform 6 is pre-curved (FIG. 5). A small, e.g. pneumatic drive motor of low power. In contrast to the prior art, no heavy masses have to be moved with great effort to pre-bend the preform. In addition, since the contact surface between the preform 6 and the receiving device 7 (cf. FIG. 4) can be made relatively small, the preform 6 looses little heat locally while holding onto the receiving device 7, so that an essentially uniformly tempered preform 6 introduced into the blow mold 21, 22 and there can be inflated with a uniform wall thickness.

In the embodiment shown, the preform 6 is only bent once (in the plane of the drawing in FIGS. 2, 3 and 5) by the pivoting of the strip part 9. In order to achieve a multiple curvature, the receiving device 7 must be articulated from several interconnected strip parts exist. It is possible not only to bend the preform 6 in one plane, that is to say two-dimensionally, but also to bend it in three dimensions. For this purpose, the hinge axis of the strip part in question must run perpendicular to the hinge axis shown in FIG. 2 between the strip parts 8 and 9. This also allows the preform 6 to be curved out of the plane of the drawing in FIGS. 2, 3 and 5. The preform 6 pre-curved in this way is then introduced into mold halves 21, 22, the recesses 20 of which are correspondingly curved in three dimensions. In this way, relatively complicated shapes of extrusion-blown hollow bodies can also be produced.

Figures 9, 10 and 11 show another embodiment of a device for receiving and pre-bending freshly extruded, hot preforms.

A receiving chain 27 is arranged below the nozzle 5 and the cutting device 18 parallel to the extrusion direction, that is to say vertically, the chain links of which are formed by blocks 28 which are connected to one another in an articulated manner. As FIG. 10 shows, for example 10 blocks 28 can be provided, of which only four blocks are visible in the broken representation of FIG. 9. Each block 28, cf. FIG. 11 has two swivel-mounted jaws 31, 32 that can be actuated by a (not shown, for example, electromagnetic or pneumatic) power drive for clamping a preform 6 (FIG. 11). Pins 33 stand from the blocks 28 from which carry guide heads 34 at their free ends. To produce an articulated chain connection, link plates 35 run in two superimposed positions between the guide heads 34 of the individual blocks 28, which are articulated to one another by bolts 37 and to the heads 34 by screw pins 36.

The receiving chain 27 is assigned a guide device 38 in the form of a curved profiled tube 39 with a C-shaped cross section. The inner cross section of the profiled tube 39 is dimensioned such that the tube can receive and guide the heads 34 of the blocks 28 with the associated articulated connections, as shown in FIGS. 10 and 11, the blocks 28 with the jaws 31, 32 on the outside of the pipe 39 are guided according to its curvature.

Furthermore, a power-operated sliding device 41 with a driver arm 42 is provided. The arm 42 can be pushed up and down in the direction of arrow C (FIG. 9) and laterally in the direction of arrow D.

By shifting to the right, the driving arm 42 is brought into engagement with the uppermost block 28 of the receiving chain 27. By moving in the direction of arrow C, the receiving chain 27 carrying a freshly extruded preform 6 is now pushed into the guide device 38. The preform 6 (FIG. 11) carried by the jaws 31, 32 of the blocks 28 is given a curvature corresponding to the guide device 38, for example white shape of a "U".

The guide tube 39 is connected via a shaft 43 to a drive motor corresponding to the electric motor 16 in FIG. 2, so that it can be folded down from the vertical position shown in FIG. 9 into the horizontal position shown in FIG. 11.

When the receiving chain 27 carrying the preform 6 has fully entered the guide tube 39, the driving arm 42 is detached (by displacement in the direction of the arrow D). Subsequently, the guide tube 39 is pivoted together with the receiving chain 27 and the pre-curved preform 6 held by it (FIG. 11), whereupon the loosened jaws 31, 32 of the preform 6 can fall into the lower mold half 21 provided. Then, as described in connection with FIGS. 1-8, the procedure is continued.

Finally, the guide device 38 is pivoted back into the vertical and the receiving chain 27 is displaced back into the position shown in FIG. 9 via the driving arm 42, so that a further preform can be extruded and taken up.

In the embodiment shown in FIGS. 9-11, the receiving chain 27 is pressed into the guide tube 39 by the driving arm 42. Instead, a pulling device, for example in the form of a wire running through the tube 39, could also be provided on the lowest block 28 of the chain 27, so that the receiving chain 27 is pulled into the guide device 38 can be introduced.

Relatively complicated, multi-curved preforms 6 can also be obtained with the aid of a guide device 38 of the type described, if only the tube 39 is bent accordingly. In particular, three-dimensionally curved preforms can also be produced with the guide device 38 if the guide tube 39 is bent in three dimensions. In this case, it is then only necessary to ensure that the articulated connection between the individual blocks 28 of the receiving chain 27 is also movable in three dimensions. For example, it is possible to pre-bend preforms in the form of a three-dimensional spiral.

As can be seen from FIG. 11, the pivotable jaws 31, 32 only engage the preform 6 with very small contact surfaces, so that the preform 6 experiences practically no heat loss during its pre-bending.

Instead of holding the preform 6 with the jaws 31, 32 on the blocks 28, the latter can also, similarly to the strip parts 8, 9 according to FIG. 4, be formed and connected to a suction device and thus hold the preform 6 under vacuum. This does not change the basic mode of action. Conversely, instead of the bores 14, the strip parts 8, 9 could also have swiveling jaws 31, 32 for holding the preform 6.

Although it has proven to be particularly cheap, the in the horizontal position brought preform (Fig. 6 and 11) from above into the lower mold half 21, it is also possible in principle to avoid folding the receiving device 7 and the guide device 38 into the horizontal and the pre-curved preform directly from one more or less vertically aligned position in the mold halves of the blow mold, the mold halves of the blow mold are then also arranged substantially vertically.

In the illustrated embodiments of the method, the curve is first pre-curved essentially in vertical planes, then the pre-curved preform 6 is folded into the horizontal. In principle, it is also possible, particularly in the embodiment according to FIGS. 1-8, to first fold the preform into the horizontal and then carry out the pre-crimping. A third possibility is to simultaneously pre-bend the preform and fold it into the horizontal.

9, a funnel or the like can also be arranged at the inlet end of the tube 39, which facilitates the insertion of the receiving chain 27. Alternatively, some blocks 28 of the chain 27 can be arranged in the vertical branch of the guide tube 39 already during the extrusion of the preform 6.

The guide device 38 can also be arranged at the end of the receiving chain 27 lying at the top in FIG. 9. The sliding device 41 then first moves the chain 27 carrying the preform 6 out of the vertical axis the nozzle 5 and then pulls the blocks 28 of the chain 27 one after the other into and through the guide device, so that the preform 6 is curved accordingly.

Claims (6)

1. A method for blow molding of curved hollow bodies made of plastic, in which a tubular preform is extruded from an extruder nozzle in a straight line vertically from top to bottom, curved, introduced into a blow mold and inflated into the hollow body therein,
characterized by
that a) the preform is extruded along a receptacle and the preform is then attached to the receptacle; b) the preform is separated after being attached to the receptacle; c) the preform is bent by changing the shape of the receptacle and d) the curved preform is introduced into the blow mold by detaching the preform from the receptacle. 2. Device for performing the method according to claim 1, with a device for bending the preform and with a blow mold consisting of two mold halves, characterized in that a) the device for curving the preform (6) has a receptacle (7, 27) extending along the extruded preform and fastening means (14; 31, 32) for fastening the preform to the receptacle; b) the receptacle (7, 27) comprises movably interconnected receptacle parts (8, 9; 28) on which the fastening means (14; 31, 32) are arranged; c) the receptacle (7, 27) can be folded from the vertical into the horizontal by means of folding means (15, 16; 43) and d) the lower one of the horizontally arranged mold halves (21) of the blow mold (2) can be adjusted to the receptacle (7, 27) folded down into the horizontal such that the curved preform (6) can be introduced into it. 3. Apparatus according to claim 2, characterized in that for attaching and pre-bending the preform (6) a length of the preform corresponding receiving strip (7) is provided, to which the preform is attachable, and that the strip of several, articulated together There are strip parts (8, 9) which can be moved relative to one another by power drive. 4. The device according to claim 2, characterized in that for attaching and bending the preform (6) articulated to a receiving chain (27) interconnected chain links (blocks 28) are provided which are movable through a guide device (38) and thereby the Bend preform. 5. Device according to one of claims 2 to 4, characterized in that on the receiving bar (7) and the blocks (28) suction openings (14) for releasably holding the preform (6) are arranged. 6. Device according to one of claims 2 to 4, characterized in that on the receiving bar (7) and the blocks (28) pivotable jaws (31, 32) for releasably holding the preform (6) are arranged.

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